1. Field of the Invention
The present invention relates to a cartridge case including a tape reel with a hub in the shape of a bottomed cylinder and a locking member that prevents rotation of the tape reel, and to an information recording medium equipped with the cartridge case.
2. Description of the Related Art
The magnetic tape cartridge disclosed by Japanese Laid-Open Patent Publication No. 2002-343058 is known as one example of this type of information recording medium. This magnetic tape cartridge is constructed by enclosing a single reel (a tape reel), around which magnetic tape has been wound, inside a cartridge case. Three pairs of engaging protrusions are disposed at equal intervals on a circle on the upper surface of the base plate of the reel hub that constructs the reel, with locking teeth being respectively formed on the ends of these engaging protrusions. A locking member that is energized in a locking direction by an energizing member is also enclosed inside the cartridge case. Locking teeth that engage the locking teeth of the reel hub are formed in a ring in an outer circumferential part of a lower surface of the locking member. When this magnetic tape cartridge is not in use, the locking teeth of the locking member and the locking teeth of the reel hub are caused to engage and thereby lock the reel in a non-rotatable state.
By investigating the magnetic tape cartridge described above, the present inventors discovered the following problem to be solved. In this magnetic tape cartridge, as shown in FIG. 13, the engaging protrusions 111a, 111b, 111c (referred to hereinafter simply as the “engaging protrusions 111” when no distinction is required) of the reel hub 101 are disposed at equal intervals on a circle, with locking teeth 112 being formed on all of the engaging protrusions 111. That is, the locking teeth 112 of the engaging protrusions 111 are formed radially about the central axis of the reel hub 101, with the ridges of the respective locking teeth 112 being shown by the solid lines in FIG. 13. The locking teeth 121 of the locking member 102 are also formed radially about the central axis of the locking member 102, with the ridges of the respective locking teeth 121 being shown by the broken lines in FIG. 13. As shown in FIG. 13, when the central axis of the reel hub 101 is coincident or substantially coincident with the central axis of the locking member 102, the orientations of the ridges of the facing locking teeth 112, 121 match one another, so that the locking teeth engage and thereby lock the reel. On the other hand, in this type of magnetic tape cartridge, a predetermined clearance is provided between the reel and the cartridge case to allow the reel to rotate smoothly. This means that when the magnetic tape cartridge is used in an inclined state, for example, there are cases where the reel moves within the cartridge case by an amount equal to the clearance. When the reel (the reel hub 101) has moved in the direction of the arrow shown in FIG. 14 for example, (to the right in the drawing), since the ridges of the locking teeth 112, 121 are formed radially as described above, as shown in FIG. 14 and FIG. 15, the orientations of the respective locking teeth 112 of the engaging protrusions 111b, 111c no longer match the orientations of the ridges of the respective locking teeth 121. This results in the tops of the locking teeth 121 riding up onto the tops of the locking teeth 112 of the engaging protrusions 111b, 111c, so that the locking member 102 does not maintain a state that is parallel to the base plate of the reel hub 101 and becomes inclined, resulting in the locking teeth 112 and 121 not engaging one another. Accordingly, with this magnetic tape cartridge, when the reel and the locking member 102 become misaligned due to movement of the reel, the reel becomes incompletely locked and can rotate, resulting in the problem that the magnetic tape wound around the reel may become slack. Also, even if the respective locking teeth 112, 121 of the reel and the locking member 102 are in complete engagement, when an external force is applied to the magnetic tape cartridge, for example, and the reel moves so that the locking teeth 112, 121 become disengaged, there is still the problem of the reel becoming incompletely locked and therefore rotating.